Magnetic amplifying circuits



y 1949- s. E. TWEEDY 2,475,575

MAGNETIC AMPLIFYING CIRCUITS Filed Oct. ,29, 1947 3 She'ets-Sheet l Q m d Zhweutor STAN LEY E. TWEEDY (Ittorncg July 5, 1949. s. E. TWEEDY 2,475,575

MAGNETIC AMPLIFYING CIRCUITS Filed on. 29, 1947 s Sheet'sSheet 2 Fias FIG 6 inventor STANLEY e1. TWEEDY y 5, 1949- s. E. TWEEDY 2,475,575

MAGNETIC AMPLIF'YING CIRCUITS Filed Oct. 29, 1947 I5 Sheqts-Sheet 3 Ihwentor STANLEY E. TW EEDY Patented July 5, 1949 Y 1 j um'rso ""STAT Es PATENT "OFFICE.

signor to Electra M a: Great Britain ethods Ltd., a corporation" In Great Britain November 2, 1946 Application October 29, 1947, Serial No. 782.777

The present invention relates to magnetic amplii'ying circuits of the kind comprising a saturable reactor combinationfor developing an amplified output power across a load impedance which output power is dependent on the value of a direct current input power, the reactor combination including a winding or windings of a selfexcitation circuit associated with a rectifier. Circuits of this kind are. known in which the output power is developed by an alternating current flowing in the load impedance, the alternating current output power being dependent on the direct current input power. Such known circuits sufier fromthe disadvantages that the output power does not easily leadto an indication of the polarity of the input power and that very precise and difllcult adjustments are necessary in order to make the output power zero when the input power is zero. It is also known by means of an additional rectifier or additional rectifiers to develop a direct current flowing in the load impedance. In this case the polarity of the output power may easily be rendered dependent on the polarity of the input power, but an additional rectifier or a plurality of additional rectifiers is required, while it -was hitherto difiicult to render the output power zero when the input power is zero, if the voltage and/or frequency of the alternating current varies.

It is an object of the present invention to avoid these disadvantages. I

According to the present invention, a circuit of the kind described is characterized in that the rectifier associated with the winding or windings of the self-excitation circuit is also associated with the load impedance and rectifies an alternating current to supply direct current to the said sat-excitation circuit as well as to the said load impedance, whereby the polarity of the direct current through said-load impedance is dependent on the polarity of the direct current input power.

Two. selfsexcitation circuits may be provided each comprising a-rectifier, the load impedance being connected so'as to' be common to the said two self-excitation circuits; in particular, two sets of saturable reactors may be provided, each setincluding. a rectifier the: alternating current terminals of whichare, when in-use, connected across windings of-the saturable reactors and an alternating current supply source, while the direct current terminals ofthe rectifiers are connected across the windings of 'theitwo self-excitation circuits and to the loadimpedance in such a manner that the direct currents derived from the rectifiers flow in opposition toeach other through the 8 Claims. (01. 321-24) 2 said load impedance for developing the output power therein.

According to another aspect of the invention, in a circuit of the kind described the output power is developed by a direct current derived from an alternating current or alternating currents and flowing in the load impedance, the circuit being characterized by the provision of means for rendering the output power substantially zero when the input power is zero, in such a manner that the output power remains substantially zero when the voltage and/or frequency of the alternating current varies within a given range. This said means may comprise an impedance or impedances connected either across one or more windings of the self-excitation circuit or across the alternating current terminals of a rectifier, and a capacitor-or capacitors connected across one or more windings in an alternating current circuit. The said impedance or each impedance may be a resistor.

To make the invention clearly understood, ref erence will now be made to the drawings accompanying the specification in which:

Fig. 1 is a circuit diagram of a known arrangement;

Figs. 2 and 3 are graphs for explanatory purposes;

Fig. 4 is a circuit diagram of an arrangement according to the invention;

Figs. 5 and 6 are graphs for explanatory purposes;

Fig. 7 is a circuit diagram of a modified arrangement of the invention; and

Fig. 8 illustrates a further modification.

All the drawings are given by way of example only. I

Referring first to Fig. 1 of the drawings, a re-v actor combination comprises twelve windings A1,

B1, C1; A2, B2, C2; A3, B3, C3; and A4, B4, C4.

Two rectifiers are each indicated by the letter R, and a load impedance is indicated by the letter L. A core of magnetic material (not shown) links windings with the same sufiix number. An alternating voltage is applied across the points A and B, the point 0 being the centre point of this voltage. The alternating current flowing through the windings A1, A2. A3, A4, is rectified by the rectiflers R, the rectified currents flowing through the windings B1, B1, B3, B4,-which serve as feed-back or self -excitation windings provided in two feed-back or self-excitation circuits. The direct current input to be amplified is applied across the input windings C1, Ca, C3, C4. The direct current flowing through the input windings 3 C1, C11, C3, 04, either assists or opposes the rectiflcd currents through the self-excitation windings B1, B1, B3, B4 and the combined magnetizing ei'Iect of the direct currents through the input and the self-excitation windings controls the eifective reactance oi the alternating current windings A1, A2, A3, A4 and, thus, the magnitude of the alternating currents therethrough, the diilerence of the alternating currents through A1, A: on the one hand and A3, A. on the other flowing through the load impedance L, said diflerence being dependent on the direct current flowing through the input windings C1, Ca, Ca, C4. However, since the load impedance L is traversed by an alternating current, no indication of the polarity of the direct current through the input windings C1, C1, C3, C4 is easily obtained by a conventional meter associated with or comprising the load impedance L. although such an indication is often desired. Moreover, while theoretically the current through the load impedance L should become zero when no current flows through the input windings, in practice this cannot or can only with great difliculties be achieved. Fig. 2 shows a graph illustrating the dependance of the alternating current (plotted as the ordinate) flowing in the load impedance L on the direct current input flowing in the input windings C1, Cz; C: and C4, it ideal conditions are assumed. In practice, however, such ideal conditions are very diiiicuit to achieve and Fig. 3 represents a typical graph obtained with circuit components subject to normal manufacturing tolerances. It is apparent that a certainalternating current represented by the distance A in Fig. 3 flows in the load impedance L when the input current is zero, the value of the alternating current being dependent on the accuracy obtainable in the manufacture of the circuit components.

It is apparent that the current flowing in the load impedance L of Fig. l is the difference between the alternating current flowing from A and that flowing into B. It is clear that both the average value aiter rectification and the root mean square value of this difference can only be zero if the instantaneous intensities of the two currents are equal to each other. Only in this case will an instrument record zero, irrespective of whether it responds to average rectifled current, such as a rectifier instrument. or v to root mean square current, such as a hot wire or moving-iron ammeter.

The present invention is based on the idea of utilizing the rectiflers R of the arrangement oi Fig. 1 also for rectifying the said two alternating currents separately, the current now flowing through the load impedance L being the diflerence between these two rectified currents. In this case, it is clearly possible to measure this diiference by means of a direct current instrument. The condition now that the instrument should read zero is that the average values of the two rectified currents causing the difference should be equal to each other. This condition is obviously much more easily-obtained than the previous condition that the instantaneous intensities of the currents should be equal to each other.

Fig. 4 illustrates an arrangement of the invention for overcoming the difllculties encountered with the known arrangement of Fig. i. In Fig. 4, two sets of saturable reactors A1, A2, B1, Ba, C1, C2 and A3, A4, B1, B4, C3, C4, are provided on cores (not shown) of magnetic material, each set being associated with a rectifier R.

flers .R are connected respectively across the series connection of the alternating current windings A1, A: and the alternating current supply source AB. and that oi the alternating current windings A3, A4 and the alternating supplysource CD, while the direct current terminals of the rectiflers R are associated with the self-excitation windings B1, B2 and B3, B4 respectively, and the load impedance L as shown in such a manner that the direct currents derived from the rectiflers R flow in opposition to each otherv through the load impedance L.

With such an arrangement, by suitably dimensioning the various components, the working characteristic of the arrangement, that is to say the relationship between the direct current in the load impedance L and the direct input current flowing in the input windings Cl, C2, C3 and C4 is typically represented by the graph oi. Fig. 5. Due to "manufacturing tolerances, the graph will generally not pass through the origin. It is, however, apparent that the polarity of the direct current in the load impedance L is dependent on the polarity as well as the magnitude or the direct input current, thereby overcoming one limitation of the known arrangement.

At first sight, it might appear from an inspection of Fig. 4 that no current at all will flow through the load impedance L whatever the magnitude of the direct current flowing through the input windings C1, C2, C3 and C4, since the load impedance L is by-passed by one or the other of the rectiflers B. This consideration, however, only applies if the rectiflers R are assumed to be ideal that is to say have an internal resistance of value zero in the direction in which they conduct. It can, however, easily be achieved that under practical workin conditions the internal resistance of the rectiflers diilers sufficiently from zero, in which case a graph like that of Fig. 5 will in fact be obtained.

For displacing the graph shown in Fig. 5 so that it passes through the origin as shown in Fig. 6 and possibly to alter the shape of the graph to some extent, a small compensating impedance may be inserted in the connection between the direct current terminals of the rectiflers R. A terminal of the load impedance L may then be connected to a point on this compensating impedance which point may be so chosen that the current in the load impedance L is zero when the input current is zero. In particular, a potentiometer may be used as such compensating impedance and the point 01' connectlon of the load impedance L to this potentiometer may be made variable. This provides a ready means of resetting the arrangement whenever the conditions, ior example the voltage and/or frequency of the aitemating supply current, change. Such an arrangement has the advantage that for a predetermined range alteration of the setting has little or no eflect on the slope of the characteristic over the linear part.

Various other means for altering the position of the characteristic are possible, for instance, the two alternating voltages applied to AB and CD may be varied in their relative magnitude.

However. each setting 0! such means is in general only correct for a particular alternating current supply voltage and frequency. An alteration of this voltage and/or frequency will usually result in the graph no longer passing through the origin.

In order to avoid this drawback, the arrangement shown in Fig. 7 may be used. The arrangement and operation of the various winds ings, the rectifiers and the load impedance are similar to those of the corresponding parts of Fig. 4 and are believed to need no further explanation. An impedance Z1 is shown which is connected across the self-excitation windings B1, B2 and an impedance Z2 is shown which is connected across the self-excitation windings B3, B4. Similarly, capacitors K1 and K2 are shown which are connected across the alternating current windings A1, A2 and A2, A4 respectively.

Assuming first that the capacitors K1 and K2 are omitted, a variation of the value of the impedance Z1, Z2 will have the efiect of altering the position and shape of the graph of Fig. 5 referred to above. In particular, by suitably choosing these values, the graph may be made to pass through the origin as shown in Fig. 6. In general, however, if now the alternating current supply voltage and/or frequency change, the graph will no longer pass through the origin, and for a given change the point of intersection of the graph with the horizontal axis will move a certain amount either to the right or to the left. When, now, the capacitors K1, K2 are added and their capacitances suitably adjusted, and, if necessary, the values of the impedances Z1 and Z2 are readjusted, it can be achieved that the point of intersection between the graph and the horizontal returns to the origin and substantially remains there when the voltage and/or frequency change each within a certain range of values.

In practice, the impedances Z1 and Z2 may be resistors. Moreover, in most cases one of the impedances Z1, Z2 and one of the capacitors K1, K2 may be omitted. The most suitable arrangement and values of the impedance or impedances and capacitor or capacitors may be found by trial and error, for example, in the following manner: For a given alternating current voltage and frequency, a resistor corresponding to the impedance Z1 is connected across the windings B1, B2. If the point of intersection moves away from the origin, the resistor is disconnected and is connected across the windings B2, B4 so that it now corresponds to the impedance Z2. If now, or if in the first instance, the point of intersection moves towards the origin, the resistance value of the resistor is varied until the point of intersection coincide with the origin.

Subsequently, the voltage of the alternating current is changed (a change of the voltage having an effect similar to that of a change of the frequency), and one of the capacitors K1, K2 is added so that again the point of intersection moves towards the origin, and its capacitance is varied until the point of intersection, again, c0- incides with the origin. Returning now to the original value of the alternating current voltage, it will in general be found that the point of intersection slightly deviates from the origin and by slightly adjusting the resistance of the resistor, the point of intersection may be returned to the origin and so on, until for both values the graph passes substantially through the origin. In most cases, it will then be found that after such an adjustment the point of intersection will substantially coincide with the origin for intermediate values of the potential of the alternating current. However, if desired or necessary, an additional adjustment or additional adjustments may similarly be effected by the use of more complicated arrangements comprising the two ca- 6 pacitors K1 and K2 and/or the two (not necessarily purely resistive) impedances Z1 and Z2.

A further modification of the invention is illustrated in Fig. 8 which will now be described: The magnetic amplifying circuit as such, that is to say, the circuit illustrated but without the circuit elements Z1, Z2, Ki, K2, is known and does in itself not form part of the present invention. The amplifier comprises as before alternating current windings A1, A2, A2, A4. self-excitation windings B1, B2, B3, B4 and direct current input windings C1, C2, C3, C4. Rectifiers R rectify the alternating currents through the alternating windings and supply direct currents to the selfexcitation windings. Two additional rectifiers V are provided for rectifying the alternating currents and supplying direct currents to a load impedance L. Again, the working characteristic of the arrangement so far described may be represented by a graph of the type shown in Fig. 5. In order to shift this graph so as to substantially coincide, independently of variations of the voltage and/ or frequency of the alternating current, with the origin, impedances Z1 and Z2 are respectively connected across the alternating current terminals of the-rectifiers R, and capacitors K1 and K2 are respectively connected across the alternating current windings A1, A2 and A3, A4. As previously explained with reference to Fig. 7, the impedances 21,122 may be resistors, and, one of the impedances Z1, Z2 and one of the capacitors K1, K2 may be omitted. The impedance or im pedances and the capacitor or capacitors are adjusted by trial and error, for example, in a similar manner as explained above with reference to Fig. 7.

Modifications of the arrangements illustrated in Figs. 7 and 8 are possible. For instance in the arrangement of Fig. '7 the impedances Z1, Z2 may be connected respectively across the alternating current terminals of the rectifiers R, While in the arrangement of Fig. 8 the impedances Z1, Z2 may be connected respectively across the self-excitation windings B1, B2 and B2, B4.

Further modifications of the arrangements of Figs. 4, 7 and 8 are possible. For example, certain 0f the windings A1, A2, A3, A4; B1, B2, B3, B4; C1, C2, C3, C4 which are shown in the drawings as separate and distinct windings, may be combined into single windings in various ways as will be appreciated by those skilled in the art.

What is claimed is:

l. A magnetic amplifier comprising a first saturable reactor having an alternating current winding, a direct current winding and a selfexcitation winding, a first rectifier having its allternating current terminals connected in circuit with a source of alternating current and. said alternating current winding and its direct current terminals connected in circuit with said self excitation winding, a second saturable reactor having an alternating current winding, a direct current input winding and a self -excitation winding, a second rectifier having its alternating current terminals connected in circuit with said source of alternating current and said second mentioned alternating current winding and its direct current terminals connected in circuit with said second mentioned self-excitation winding,

a load impedance connected in common with said first and second mentioned self-excitation circuits and said first and second rectifiers, the said load impedance being energized by said rectifiers in opposition and means for maintaining the output power in said load impedance substantially zero when the power applied to said direct current input windings is zero regardless oi variations in frequency or voltage of said alternating current source.

2. A magnetic amplifier as defined in claim 1 in which said means for maintaining said output power substantially zero comprises an impedance connected across one of said self-excitation windlugs and a capacitor connected across one of said alternating current windings.

3. A magnetic amplifier as defined in claim 2 in which the impedance connected across one of said self-excitation windings is a resistor.

4. A magnetic amplifier as defined in claim 1 in which said means for maintaining said output power substantially zero'comprises an impedance connected across the alternating current terminals of one of said rectifiers and a capacitor connected across one of said alternating current windings.

5. A magnetic amplifier as defined in claim 4 in which the impedance connected across the alternating current terminals of one of said rectlfiers is a resistor.

6. A magnetic amplifier as defined in claim 1 in which said means for maintaining the power output substantially zero comprises impedances connected across said first and second mentioned self -cxcitation windings and capacitors connected across said first and second mentioned alternating current windings.

7 A magnetic amplifier as defined in claim 1 in which said means for maintaining the power output substantially zero comprises impedances connected across the alternating current terminals of each of said rectifiers and capacitors connected across said first and second mentioned alternating current windings.

8. A magnetic amplifying circuit of the saturable reactor type energized by an alternating current source wherein an amplifier power output is developed across a load impedance which power output is dependent on the value of a direct current input comprising, a first saturable reactor, a self-excitation circuit therefor including a selfexcitation winding and a rectifier connected to said alternating current source, a second saturable reactor, a self-excitation circuit for said second saturable reactor including a self-excitation winding and a rectifier connected to said alternating current source, a circuit including said load impedance connected in common with said first and second self-excitation circuits and means for maintaining the output power substantially zero when the power applied to said direct current input is zero regardless of variation in frequency or voltage of said alternating current source.

STANLEY EDWIN TWEEDY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,844,704 Thompson Feb. 9, 1932 1,955,322 Brown Apr. 17, 1934 1,973,055 Fitz Gerald Sept. 11, 1934 2,036,708 Logan Apr. 7, 1936 

